Treatment of sour hydrocarbons with caustic solutions



8 0 o 3 s ,w 2 T U L O S C I T S U A C H T I w S N O B R An C O R D V. H R U O S F O T N E M T An E Dn T Dec. 23, Y1952 L.. D. KLElss Filed Dec. 2o, 1949 INVENTOR.

L.D. KLEISS ATTORNEYS HBddIUlS WVlLS HENEMDIHL Patented Dec. 23, 1952 TREATMENT OF SOUR HYDROCARBN S WITH CAUSTIC SOLUTIONS Louis D. Kleiss, Phillips, Tex., assignor to Phillips Petroleum Company, a corporation of Delaware Application December 20, 1949, SeralNo. 134,079

6 Claims.

This invention relates to a novel process for the removal, concentration and recovery of mercaptans present in a hydrocarbon material, for example, a gasoline. In one of its aspects the invention relates to an integrated process comprising certain novel steps and combinations which can be employed to remove, concentrate and recover mercaptans, and the like, from a hydrocarbon material, for example a gasoline. In another of its aspects the invention relates to a process for the removal, concentration and recovery of meroaptans from a hydrocarbon material employinga rather high concentration liquid treating agent which is readily adapted to its purpose and which can be readily and economically regenerated for reuse. In still another of its aspects the invention relates to a mercaptan removal, concentration and recovery process inwhich there is employed a resulting mercaptide concentration and separation step. A still further aspect of the invention is that which relates to a novel step employed to prevent clogging of the equipment at certain places in certain manners.

The treatment of hydrocarbons, for example gasoline, with caustic alkali has been practiced in the petroleum art for some time. Thus, it is known to treat a sour gasoline with solutions of caustic soda or with solid caustic soda. When a solution has been used, its concentration has been low, usually of the order of up to 30 per cent. The removal of the undesirable sulfur compounds, in order to sweeten a sour gasoline, has been reported to be less complete, with the solutions of caustic soda which have been used,

than with the anhydrous material. Thus, the present practice, in which sludging of the caustic solution is sought to be avoided by using a low concentration of caustic, does not effect a complete mercaptan removal but eiiects the removal of only the lighter mercaptans. Furthermore, in treating a hydrocarbon fraction with a weak alkaline solution, oftentimes, there is encountered a loss of materials due to emulsication of the hydrocarbon and reagent by soaps which are formed. Still further, the quantity of water in the weak caustic solutions which are currently used presents an uneconomical handling problem and expense. When anhydrous caustic is used the problems which will be involved in its dispersion in I the hydrocarbon and in its regeneration and concentration are at once obvious to one skilled in the art. Thus, to mention only one major problem, the transfer of anhydrous caustic Jfrom one point of the treating unit to another almost, if not actually, renders its use prohibitive.

It has now been found, according to this invention, that a solution of caustic alkali having a concentration of from 56 to 80 per cent by Weight, preferably 60 to 75 per cent by weight, if

(Cl. 19E-32) mixed thoroughly with a sour hydrocarbon gasoline stock will cause the substantially complete removal of all of the mercaptans in said stock forming mercaptides which separate from the hydrocarbons as a precipitate. Further, according to the invention, it has been found that the removal and precipitation of the mercaptans as mercaptides can be completely eiiected by preheating the hydrocarbon to a temperature in the range to 300 F., preferably 120 to 200 F. and then admixing it thoroughly with a caustic solution of desired concentration which is at a temperature in the range of 100 to 300 F. pre1- erably to 200 F., depending upon its concentration to the extent that the caustic solution shall always be fluid in character, follow.- ing which the admixture is chilled, whereupon at least a part of the caustic solution is solidified in a dispersed form having a high surface area. Still according to the invention, and as a feature` thereof, the chilling is effected employing unheated hydrocarbons available in the process. Still further, according to the invention, a thickener, such as a Dorr thickener, is employed to cause agglomeration and concentration of the precipitated mercaptides and caustic solids which can then be treated with steam, or otherwise, to recover mercaptans and to regenerate the caustic solution for reuse.

It is to be noted that when the process of the present invention is employed caustic loss due to emulsiication can be reduced, because its concentration is suicient to salt out any soaps which may be formed, removal of the mercaptans will be as complete as it is with solid caustic, and that regeneration and reconcentration Will be easier and more efficient because, the caustic solution will be uid at the temperature at which it is found in the process except in the cooling and agglomeration steps. It should be further noted that the concentration of caustic employed in the process of the invention is such that the caustic can be pumped conveniently when heated by plant steam which is usually available at a temperature in the range of 210 to 360 F.

The feature of employing a thickener is especially valuable because this makes it possible to agglomerate and to separate the sludge of solidifled caustic solution and precipitated mercaptides from the sweetened hydrocrabon. This sludge may be thereafter conveyed by means of steam jets, or otherwise.

Thus, according to this invention, there has been provided a process for the treatment or a hydrocarbon fraction for the removal of mercaptans therefrom which comprises the steps of heating said fraction to a temperature in the range of 100 to 300 F., admixing with it a caustic solution having a concentration in the range of 56 to 80 per cent by weight and at a temperature in the range of 100 to 300 F., chilling the said admixture to cause the formation of precipitated mercaptides and solid caustic solution particles of high surface area and then separating the mercaptide free hydrocarbon fraction from the caustic solution and said mercaptides. Still further according to the invention the mercaptides and solid caustic solution can be agglomerated and concentrated along with any liquid caustic solution present by means of a thickener following which regeneration of the mercaptans and the caustic solution for reuse can be effected. Still further according to the invention the chilling can be effected employing unheated, treated or untreated hydrocarbon available in the process.

Reference is now made to the drawing which shows a diagrammatic ow-plan of an embodiment of a process according to the invention.

Preheated sour hydrocarbon such as gasoline or an oil, is introduced to the suction of the mixing pump which also draws caustic solution from the caustic surge tank. In the pump the caustic solution and the hydrocarbon are thoroughy admixed to cause intimate contact between them. The caustic from the caustic surge tank is supplied to the mixing pump at a temperature such that at a concentration, which is in the range of from about 56 to about S0 per cent by weight, the caustic will be fluid and pumpable. temperature will be in the range of 100 to 300 F. Just before the admixture of hydrocarbon and caustic solution is discharged into the thickener there is admixed therewith a relatively cold or unheated hydrocarbon, for example, some of the sweetened hydrocarbon of the process. This is shown to be the case in the drawing. Clearly the chilling can be effected by a hydrocarbon, or equivalent material, from another source, although the step as shown, is preferred. The chilling step not only assists in the precipitation of mercaptide but it also prevents plugging of the discharge pipe into the thickener. In the preferred operation of the invention, the chilling fluid is introduced annularly to further insure that there shall be no deposition and consequent clogging of the discharge pipe. The thickener can be operated in a conventional manner to agglomerate and to coagulate the precipitated mercaptide and solid caustic particles which can be steam jet or screw conveyed together with any liquid caustic solution to the steam stripper for regeneration of the mercaptans and the caustic solution. Mercaptans are taken off overhead with steam and the caustic bottoms are concentrated in the caustic evaporator from which the regenerated and reconcentrated caustic is passed into the caustic surge tank. sweetened hydrocarbon is drawn off overhead from the thickener, cooled and sent to storage. Some of the cooled hydrocarbon can be recycled as the chilling medium, as shown.

The reaction which takes place in the process of the present invention is known and can be represented as follows.

The relatively high caustic concentration of the invention is believed to be advantageous, as set forth, because it is believed that th-e increased concentration of caustic will drive the reaction, which is reversible, to the right and by absorption of water which is formed thus further drive the reaction to the right. Chilling also drives the reaction to the right. Thus it is that the Thus the present invention is believed to permit the realization of the advantages of anhydrous caustic while avoiding its disadvantages as well as the realization of the advantages of the heretofore used low caustic concentration while avoiding its disadvantages all as set forth and fully described herein.

Variation and modification are possible within the scope of the foregoing disclosure and appended claims to the invention the essence of which is that a caustic solution having a concentration in the range of 56 to 80 per cent by `weight and at a temperature in the range of to 300 F. is admixed with a sour hydrocarbon stream preheated to a temperature in the range 100 to 300 F. The admixture is then chilled to cause the formation and precipitation of mercaptides which are then separated together with the caustic from the resulting sweetened hydrocarbon and a. special feature of which is that the chilling is effected at the discharge of the admixing means, preferably annularly of the discharge pipe and also that a thickener of the Dorr type is employed to agglomerate and concentrate the precipitated mercaptide which can then be removed from the thickener together with the excess caustic and sent to a caustic regeneration zone wherein the mercaptan is recovered, as such, and the caustic is recovered and regenerated for reuse.

I claim:

1. A process for sweetening of a sour hydrocarbon fraction which comprises preheating said hydrocarbon fraction, admixing said hydrocarbon fraction with a caustic solution having a concentration in the range of from 56 to 80 per vcent by weight and having a temperature in the range of 100 to 300 F., chilling said admixture to a temperature at which solid caustic is formed and mercaptides are precipitated therewith and separating the resulting mercaptide and solid caustic admixture from the thus sweetened hydrocarbon.

2. A process according to claim 1 wherein the chilling is effected by injection of and consequent admixture of a relatively cold or unheated hydrocarbon fraction with the admxed hydrocarbon and caustic solution as it leaves the admixing step.

3. A process according to claim 2 wherein said chilling medium is a hydrocarbon fraction available in the process.

4. A process according to claim 3 wherein said hydrocarbon fraction is at least a portion of said sweetened hydrocarbon.

5. A process according to claim 1 wherein the precipitated mercaptide and caustic solids are LOUIS D. KLEISS.

REFERENCES ICITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,756,153 Herthel Apr. 29, 1930 2,311,593 Kalichevsky et al. Feb. 16, 1943 2,317,053 Henderson Apr. 20, 1943 

1. A PROCESS FOR SWEETENING OF A SOUR HYDROCARBON FRACTION WHICH COMPRISES PREHEATING SAID HYDROCARBON FRACTION, ADMIXING SAID HYDROCARBON FRACTION WITH A CAUSTIC SOLUTION HAVING A CONCENTRATION IN THE RANGE OF FROM 56 TO 80 PER CENT BY WEIGHT AND HAVING A TEMPERATURE IN THE RANGE OF 100* TO 300* F., CHILLING SAID ADMIXTURE TO A TEMPERATURE AT WHICH SOLID CAUSTIC IS FORMED AND MERCAPTIDES ARE PRECIPITATED THEREWITH AND SEPARATING THE RESULTING MERCAPTIDE AND SOLID CAUSTIC ADMIXTURE FROM THE THUS SWEETENED HYDROCARBON. 